The other day I reached in my pocket for my phone, and it was hot. It had gone from a full charge to dead battery in 2 hours. I wrote it off as an app gone nuts. When it happened again a couple days later, I started to investigate.
After a lot of experiments, I think I tracked it down to Google Reader. I use Reader a lot, and I often leave it running in Safari Mobile. I'm thinking javascript went crazy as I've seen on the desktop once in a while. This is surprising since I thought Safari fully paused when not active, but every time this happened I had completed a long reader session and left it running.

Bottom line is to be careful leaving any javascript-heavy pages loaded in Safari all the time. Be especially careful of those that automatically phone home.

I'll keep an eye open, but so far my battery is much happier when I don't leave Reader running.